In the manufacture of a liquid crystal display element, a semiconductor element such as an IC, or the like, a thin film forming process is indispensably necessary so as to form a thin film of a metal, an insulating material, or the like on a substrate thereof. In this process, a film forming method is often performed by a sputtering apparatus that uses a raw material for thin film formation as a target, converts an argon gas or the like into a plasma by DC high voltage or high-frequency power, and activates the target by the plasma-converted gas so that the target is melted and dispersed to be coated on a substrate to be processed.
Such a sputtering film forming method tends to be mainly directed to a film forming method which uses a magnetron sputtering apparatus in order to raise the film forming rate. Specifically, the magnetron sputtering apparatus has magnets disposed on the back side of a target to generate the lines of magnetic force parallel to a target surface and to thereby confine plasma to the target surface to obtain high-density plasma.
FIG. 11 is a diagram for explaining the structure of the main part of a magnetron sputtering apparatus according to the prior art described above, wherein 101 denotes a target, 102 a substrate to be formed with a thin film, 103 a plurality of magnets, 104 lines of magnetic force, and 105 regions where the target 101 is melted and separated, i.e. erosion regions.
As shown in FIG. 11, the plurality of magnets 103 are disposed on the back side of the target 101 with their N-poles and S-poles oriented in predetermined directions, respectively, and the high-frequency power (RF power) 106 or the DC high-voltage power 107 is applied between the target 101 and the substrate 102 to excite a plasma on the target 101.
On the other hand, around the plurality of magnets 103 disposed on the back side of the target 101, the lines of magnetic force 104 are generated toward the S-poles from the adjacent N-poles. At a position where a vertical magnetic field (magnetic force line components perpendicular to a target surface) is zero on a target surface, a horizontal magnetic field (magnetic force line components parallel to the target surface) becomes locally maximum. In a region where the amount of horizontal magnetic field components is large, electrons are captured near the target surface to form high-density plasma, and thus, the erosion region 105 is formed at this position centered.
Since the erosion regions 105 are each exposed to high-density plasma as compared with the other regions, the target 101 is intensively consumed. When the film formation is continued so that the target material is used up in these regions, it is necessary to replace the entire target. As a result, the utilization efficiency of the target 101 becomes low and further there is a tendency that, with respect also to the thickness of a thin film on the substrate 102 disposed facing the target 101, the film thickness at positions facing the erosion regions 105 becomes greater so that the film thickness uniformity over the entire substrate 102 is deteriorated.
Further, since the erosion regions 105 are consumed, the distance between the target surface in the erosion regions and the magnets 103 becomes near as the consumption proceeds. Since the magnetic field strength becomes strong as the distance to the magnets becomes short, plasma with a higher density is excited in the erosion regions as compared with that before the consumption of the target. Therefore, a problem takes place such that, during long-term use, the film forming rate changes with time and the utilization efficiency degrades due to further local target consumption.
In order to suppress the time-dependent change in film forming rate, it is effective to move the magnets 103 away from the initial surface of the target depending on the consumption of the target (Non-Patent Document 1). However, when the consumption of the target is nonuniform, even if the distance between the magnets 103 and the initial surface of the target is increased by an amount corresponding to the consumption of the erosion regions, the magnetic field strength distribution on the surface of the target after the consumption differs from the initial magnetic field strength distribution even in the erosion regions because these regions are consumed in a smooth concave shape. Therefore, it is necessary to uniformly consume the target for suppressing the time-dependent change in film forming rate.
In view of this, there have conventionally been proposed techniques of using bar magnets as magnets for generating magnetic fields and moving erosion regions with time by moving or rotating the bar magnets, thereby substantially preventing local consumption of a target on the time average and further improving the film thickness uniformity of a substrate (see Patent Documents 1 to 3).    Non-Patent Document 1: Canon ANELVA Technical Report vol. 12 (pp. 29-32)    Patent Document 1: JP-A-H5-148642    Patent Document 2: JP-A-2000-309867    Patent Document 3: JP-B-3566327